C02 and PH question

[aquarium 308]

I got a 40 gallon that I hooked up a co2 kit on. My first time using c02. Question is that I calibrated my mikwaulkie controller and it was reading my water to be 7.5 ph. I started dosing co2 at about 1 bubble or less a second. After about 12 hours my ph read 7.9 ph. Should my ph be going the other direction which is down instead of up.
Thanks
Nick

 

[Delapool]

Lol, yes - ph should be going down. Do you have another ph test kit to check?

I have the Ista ph controller so can't help but did the calibration go ok?

 

[Fresh2o]

Yes, that is odd. Should be dropping. I agree, test it independently over the course of the day (API pH and High pH tests kits as a recommendation).
I finally tested my morning versus evening pH and I am getting a 1.2-1.4 drop during the day at ~2 bps using a GLA knockoff diffuser placed in the path of my canister output (heavy mist in the water column).

 

[aquarium 308]

Yes calibration was easy and hardly needed any adjustment. I do have driftwood in the aquarium which is leasing tannins in the water. Also just before staring the co2 for the first time yesterday I did a 25 percent water change.